1. Field of the Invention
This invention relates to a synchrotron radiation apparatus capable of extracting electromagnetic waves emitted when high energy electrons are deflected by a magnetic field.
2. Description of the Related Art
As is well known in the art, the integration density of a semiconductor device is largely dependent on the wavelengths used in an exposure light source. At present, ultraviolet rays are used as the exposure light but it has become extremely difficult to further enhance the integration density by use of the above exposure lights.
With the above problems taken into consideration, recently, various studies have been conducted to use electromagnetic waves (specifically, soft X-rays) emitted when high energy electrons are deflected by a magnetic field and having a large directivity as the exposure light. Actually, some proposals relating to a synchrotron radiation apparatus capable of emitting such an exposure light have been made.
In general, the synchrotron radiation apparatus is constructed to inject high energy electrons accelerated by a pre-accelerator into an accumulation ring held in a vacuum condition, deflect and circulate the injected high energy electrons by use of a plurality of deflection electromagnets mounted along the accumulation ring, and derive out soft X-rays emitted when the high energy electrons are deflected.
In order to simplify application of the synchrotron radiation apparatus in the LSI manufacturing field, for example, some improvements must be made. For example, in the conventional synchrotron radiation apparatus, since the lifetime of low energy electrons is considered to be short, the electrons are accelerated to several hundreds MeV or more by means of a pre-accelerator and the high energy electrons are injected into the accumulation ring and gradually accelerated to the rate energy. Alternatively, the electrons are injected into the acceleration ring at 100 MeV or less and then rapidly accelerated to the rate energy in the acceleration ring, and re-injected into another accumulation ring. In the base cases, since the pre-accelerator used is large, the size of the whole synchrotron radiation apparatus becomes large.
Further, in the conventional synchrotron radiation apparatus, a core called a rectangular type is used as the core for the deflection electromagnets. The core may be formed by laminating a large number of thin plates punched in a form corresponding to the cross section of the core or "rectangular C"-shaped form, for example, into a sector configuration along the electron track. Alternatively, a core called a sector type core formed by laminating a large number of thin plates punched in a "rectangular C"-shaped form into a sector configuration outside the defection track with spacers disposed therebetween may be used as the core for the deflection electromagnets.
However, in sector type core, the cross sectional width of each of the magnetic poles on the electron track side and the cross sectional width of the return yoke are made substantially equal to each other, and the area of the magnetic flux path of the return yoke is made small. It, therefore, becomes difficult to raise the magnetic field to 1.5 T which is considered to be the maximum available magnetic field for the core material and reduce the circumferential length of the accumulation ring by intensifying the deflection magnetic field.
As described above, in the conventional synchrotron radiation apparatus, it is difficult to reduce the size of the whole synchrotron radiation apparatus and accumulate electrons of sufficient amount of energy in the accumulation ring.